This invention relates to the therapeutic uses of oligomers of 15-dehydroprostaglandin B.sub.1 and oligomers of 16, 16'-dimethyl-15-dehydro PGB.sub.1 and oligomers of other 16 carbon substituted 15-dehydro PGB.sub.1 compounds (hereinafter referred to as oligomers of PGB.sub.1) in tissue ischemia, hypoxia and anoxia, (hereinafter referred to collectively as tissue ischemia) and in protecting isolated organs (hearts, kidneys etc.) and cells (whole blood, erythrocytes, platelets, etc.) during in vitro transfer and storage; and as a pharmacological agent in abnormal conditions in humans and animals in which alteration in cellular calcium is a mediator in the disease process.
The derivatives of 15-dehydroprostaglandin B.sub.1 described in this disclosure include oligomeric forms of the parent 15-dehydroprostaglandin B.sub.1 and of the 16, 16'-dimethyl-15-dehydroprostaglandin, both series of which have been synthesized in co-pending application Ser. No. 769,045, filed Aug. 23, 1985 1985, inventor: George Nelson, the entire disclosure of which is incorporated herein by reference, and of other oligomeric forms from derivatives in which there has been a substitution on carbon 16 of the 15-dehydroprostaglandin. The specific oligomeric forms include the dimer, trimer, tetramer and pentamer and mixtures thereof. Henceforth, they will be referred to generically as oligo-PGB.sub.1.
Prostaglandin (PGB.sub.x), as set forth in Polis U.S. Pat. Nos. 4,153,808 and 4,245,111 has been determined to be useful for a wide variety of in vivo and in vitro adverse biological conditions, including the reversal of degenerative changes in mitochondria, the protection of the heart against cardiac insults, the protection and reversal of anoxic damage to the brain, and the improvement of mammalian performance for conditioned physicological tasks. Such prostaglandin (PGB.sub.x) is prepared by the base catalyzed reaction of PGB.sub.1 as set forth in Polis U.S. Pat. No. 4,153,808. An improved method for synthesizing and purifying PGB.sub.x which is defined in Polis U.S. Pat. No. 4,245,111 as a mixture of polymers of prostaglandin B.sub.1, involves utilizing solutions of (1) 15-keto PGB.sub.1 methyl ester in ethanol and (2) 2 N KOH solution.
However, PGB.sub.x as prepared by the method of both Polis patents, is a complex mixture. It was not possible to isolate the actual active components. Moreover, the Polis processes for syntheses of PGB.sub.x was very drastic and not specific, leading to a variety of compounds and degradation products. Quality control on the Polis processes was difficult and each batch of PGB.sub.x could vary significantly, reducing its value as a therapeutic agent. On the other hand, the defined oligo PGB.sub.1 's of the present invention are known structures wherein the synthetic procedure, as set forth in the aforesaid Nelson pending patent application, can be monitored for impurities.
Moreover, the defined structures of the oligo PGB.sub.1 's of the present invention also permit critical evaluation of the human and animal toxicity of the individual oligomers. The metabolic disposition of the drug can be evaluated because radiolabeled material can be prepared for preclinical drug evaluation with the assurance that the labeled material is the drug and not inactive contaminants as might occur in PGB.sub.x.
The foregoing properties of the present invention are in sharp contrast to the products produced by the methods of the Polis patents. As previously stated, the Polis procedures were very drastic and the Polis products contained an unknown number of differing compounds of varying size, wherein the most active fraction had a mean molecular weight of 2200-2400. It has not been feasible to purify such materials or to determine the chemical structures of the various components. Although the mixture of PGB.sub.x of Polis has been evaluated as a protective agent in tissue ischemia with some success, the striking disadvantages of PGB.sub.x as set forth hereinabove, have rendered it generally unusable. It is improbable that the active components of PGB.sub.x will ever be isolated or identified, thus, making PGB.sub.x an unlikely candidate for development as a drug. The passage of approximately ten years has further confirmed the foregoing.
It is known that an ischemic condition occurs when the circulation to a tissue or organ is impaired. Such condition can be caused by a collapse of the circulation, a blockage of blood flow to the tissue by an embolism or clot of an artery supplying a tissue, or by a reduction in the blood volume or blood pressure such as occurs in shock. The condition leads to first a hypoxic (low oxygen) then to an anoxic (no oxygen) condition. Tissue without adequate blood supply cannot receive adequate nutrients or remove toxic waste products of metabolism.
A series of degenerative changes occur in the tissue subjected to ischemia which are initially reversible but with time become irreversible. The condition leads to an infarction in the tissue in which the cells die and the tissue becomes necrotic. All tissues are potentially subject to the problems of ischemia, but those conditions which are most life threatening are when ischemia occurs to the heart (myocardial infarct or heart attack), brain (stroke), kidney, spinal cord and lung.
Ischemic conditions of other tissues are also clinically significant, including the stomach, (gastric ulcers) and intestines (necrosis) and during surgery where the blood supply may be temporarily disrupted. The most important time for therapeutic intervention is the period immediately following the ischemic phase, when the tissue is attempting to adapt to the changed blood supply and reperfusion of the tissue by blood is occurring. If the tissue cannot survive the post-ischemic period, then cell and tissue death occurs.
Most tissues do not regenerate readily, thus the function of the organ can be compromised, and, depending on the organ, serious neurological and/or physical impairment and death of the tissue and individual can occur. At the cellular level, the loss of the blood supply deprives the cells of oxygen.
At the morphological level, there is a disorganization of cellular structures, a swelling of cell organelles particularly mitochondria, membrane disruption and lysis of cellular organelles. Of particular importance are the changes in mitochondria, which utilize oxygen to supply the cells with chemical energy. Swelling of mitochondria leads to a potentially irreversible damage of the chemical mechanism of energy production (oxidative phosphorylation).
A consequence of the foregoing loss is the inability of mitochondria to participate in the control of intracellular calcium levels. An increase in calcium triggers a number of potentially deleterious reactions, including stimulation of specific hydrolytic reactions involving arachadonic acid formation (phospholipase A.sub.2). Arachadonic acid is the precursor for prostaglandins, prostacyclin, thromboxanes and leucotrienes; these metabolites have a variety of effects on cellular activities.
Very similar morphological and biochemical changes occur to many tissues and cells during storage in vitro. During the period between removal of an organ (e.g., heart, kidney, liver, etc.) from a donor and transplant into a recipient, the organ is subject to the same changes as observed in ischemia of organs in situ.
The changes observed in mitochondria in situ are also observed with mitochondria isolated from tissues. Freshly isolated mitochondria free of other cellular components have the characteristics of mitochondria in a tissue. When incubated in vitro in a reaction system for measuring their biochemical activities they maintain these in situ characteristics, but after 20-30 minutes they begin to swell and there is a loss of their ability to utilize oxygen, carry out oxidative phosphorylation, maintain their membrane potential, and maintain the intramitochondrial calcium. Isolated mitochondria can be employed to study the effectiveness of agents in protecting against tissue ischemia.
It will be seen that the present invention recognizes therapeutic uses of defined chemical compounds which would have a protective role on a tissue during ischemia and/or during the immediate post-ischemic period. Accordingly, the present invention provides for therapeutic uses of important pharmacological agents and reduces the risk of permanent disability and death. Such therapeutic uses of compounds are also valuable in storing of tissues during transplant and the storage in vitro of cells such as platelets or erythrocytes.